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Aspects on Interference and Diversity in Wireless Networks

Florén, Fredrik LU (2005) 54.
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling behandlar två ämnen inom trådlös kommunikation: interferens mellan frekvenshoppande (FH) nätverk och fleranvändardiversitet.



I arbetet på FH nätverk undersöks ett system där frekvenshopp används för att möjliggöra samtidig tillgång till kanalen för multipla okoordinerade nätverk. Detta åstadkoms genom att frekvenshoppen sker varje gång ett ny paket skall skickas, och genom att låta sekvensen av hoppfrekvenser vara pseudo-slumpmässig. Utöver detta tillåts nätverken i det undersökta systemet att använda multipla pakettyper, vilka kan ha olika längder. En genomströmningsanalys av detta system genomförs och denna analys baseras huvudsakligen på två antaganden. Det... (More)
Popular Abstract in Swedish

Denna avhandling behandlar två ämnen inom trådlös kommunikation: interferens mellan frekvenshoppande (FH) nätverk och fleranvändardiversitet.



I arbetet på FH nätverk undersöks ett system där frekvenshopp används för att möjliggöra samtidig tillgång till kanalen för multipla okoordinerade nätverk. Detta åstadkoms genom att frekvenshoppen sker varje gång ett ny paket skall skickas, och genom att låta sekvensen av hoppfrekvenser vara pseudo-slumpmässig. Utöver detta tillåts nätverken i det undersökta systemet att använda multipla pakettyper, vilka kan ha olika längder. En genomströmningsanalys av detta system genomförs och denna analys baseras huvudsakligen på två antaganden. Det första antagandet säger att kollisioner, dvs överlapp i tid och frekvens mellan paket, alltid orsakar en total förlust av data i de kolliderande paketen. Det andra antagandet säger att nätverken är asynkrona. Både exakta och approximativa uttryck för genomströmningen tas fram och genomströmningens beroende på antalet nätverk och de tillgängliga pakettyperna undersöks för två existerande system, nämligen Bluetooth och IEEE 802.11 FHSS. Utöver detta undersöks noggrannheten av kollisionsantagandet som funktion av avståndet mellan nätverk för Bluetooth-systemet.



Det andra ämnet i denna avhandling, fleranvändardiversitet, är ett system där en basstation, via en returkanal, mottar information om kanalkvalitén från ett antal användare och sedan skickar information till den användare som har den momentant bästa kanalen. Detta system ger stora vinster men det finns ett antal praktiska aspekter som kommer att reducera dessa vinster. I denna avhandling behandlas två av dessa aspekter. För det första undersöks inverkan av att kvantisera de mätningar av signal-till-brus-förhållandet som användarna skickar tillbaka till basstationen. Detta görs för transmission med både variabel och konstant takt. Resultaten visar att även för en grov kvantisering är vinsten med fleranvändardiversitet betydlig och god prestanda erhålls. För det andra undersöks inverkan av fördröjning i returkanalen. Denna analys inkluderar även andra former av diversitet, nämligen frekvensdiversitet, som erhålls mha Rake-mottagare, eller sändardiversitet, som erhålls mha "space-time block codes". Dessa former av diversitet kallas här länkdiversitet. Uttryck för felhalter och spektraleffektiviteter härleds för okodad transmission med både konstant och variabel takt, och beroendet på antalet användare, fördröjningen och länkdiversitetsordningen undersöks. Dessa uttryck kan även användas för system där Rake-mottagare kombineras med antennselektion på sändar- eller mottagarsidan. (Less)
Abstract
This thesis deals with two topics in wireless communications: interference between frequency-hopping (FH) networks, and multiuser diversity.



The work on FH treats a system where FH is used to provide simultaneous access to the channel for multiple uncoordinated wireless networks. This is achieved by performing frequency hops on a packet-by-packet basis, and letting the sequence of hopping frequencies be pseudo random. Furthermore, the networks in the considered system are allowed to use several packet types, which can be of different lengths. A throughput analysis of this system is performed, and this analysis is based mainly on two assumptions. Firstly, collisions, i.e., overlaps in time and frequency between packets,... (More)
This thesis deals with two topics in wireless communications: interference between frequency-hopping (FH) networks, and multiuser diversity.



The work on FH treats a system where FH is used to provide simultaneous access to the channel for multiple uncoordinated wireless networks. This is achieved by performing frequency hops on a packet-by-packet basis, and letting the sequence of hopping frequencies be pseudo random. Furthermore, the networks in the considered system are allowed to use several packet types, which can be of different lengths. A throughput analysis of this system is performed, and this analysis is based mainly on two assumptions. Firstly, collisions, i.e., overlaps in time and frequency between packets, are assumed to always result in a total loss of the data in the colliding packets. Secondly, it is assumed that networks are asynchronous. Both exact and approximate expressions for the throughput are derived, and the dependence of the throughput on the number of networks and the available packet types is investigated for two existing wireless systems, namely Bluetooth and IEEE 802.11 FHSS. Furthermore, the accuracy of the collision assumption as a function of the distance between networks is determined for the Bluetooth system.



The second topic of this thesis, multiuser diversity, is a scheme where a base station collects channel state information from a number of users and then transmits to the user with the instantaneously best channel. Although this scheme promises large gains, there are a number of practical aspects that reduce this gain. In this thesis two of these aspects are considered. Firstly, the impact of quantizing the feedback of the users' signal-to-noise ratio measurements is investigated for both variable- and constant-rate transmission. It is shown that even for a coarse quantization, the multiuser diversity gain is significant and good performance is achieved. Secondly, the impact of feedback delay is analyzed while also taking into account the additional diversity, referred to as link diversity, that Rake reception or transmit diversity (using space--time block codes) can provide. Expressions for the error rates and spectral efficiencies for uncoded constant- and variable-rate transmission are derived, and the dependence on the number of users, the feedback delay, and the link diversity order is investigated. These expressions also apply to Rake reception combined with transmit or receive antenna selection. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Sternad, Mikael, Uppsala Universitet
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Telekommunikationsteknik, Telecommunication engineering, Elektronik och elektroteknik, Electronics and Electrical technology, feedback, multiuser communication, diversity, throughput, packet radio networks, Interference, frequency hop communication
volume
54
pages
218 pages
publisher
Department of Electroscience, Lund University
defense location
Room E:1406, E-building, Ole Römers väg 3, Lund Institute of Technology.
defense date
2005-09-30 10:15
ISSN
1402-8662
language
English
LU publication?
yes
id
0c64a39c-1cd6-4d77-ba6d-ee56517a9ee4 (old id 545351)
date added to LUP
2007-09-06 16:17:59
date last changed
2016-09-19 08:44:59
@phdthesis{0c64a39c-1cd6-4d77-ba6d-ee56517a9ee4,
  abstract     = {This thesis deals with two topics in wireless communications: interference between frequency-hopping (FH) networks, and multiuser diversity.<br/><br>
<br/><br>
The work on FH treats a system where FH is used to provide simultaneous access to the channel for multiple uncoordinated wireless networks. This is achieved by performing frequency hops on a packet-by-packet basis, and letting the sequence of hopping frequencies be pseudo random. Furthermore, the networks in the considered system are allowed to use several packet types, which can be of different lengths. A throughput analysis of this system is performed, and this analysis is based mainly on two assumptions. Firstly, collisions, i.e., overlaps in time and frequency between packets, are assumed to always result in a total loss of the data in the colliding packets. Secondly, it is assumed that networks are asynchronous. Both exact and approximate expressions for the throughput are derived, and the dependence of the throughput on the number of networks and the available packet types is investigated for two existing wireless systems, namely Bluetooth and IEEE 802.11 FHSS. Furthermore, the accuracy of the collision assumption as a function of the distance between networks is determined for the Bluetooth system.<br/><br>
<br/><br>
The second topic of this thesis, multiuser diversity, is a scheme where a base station collects channel state information from a number of users and then transmits to the user with the instantaneously best channel. Although this scheme promises large gains, there are a number of practical aspects that reduce this gain. In this thesis two of these aspects are considered. Firstly, the impact of quantizing the feedback of the users' signal-to-noise ratio measurements is investigated for both variable- and constant-rate transmission. It is shown that even for a coarse quantization, the multiuser diversity gain is significant and good performance is achieved. Secondly, the impact of feedback delay is analyzed while also taking into account the additional diversity, referred to as link diversity, that Rake reception or transmit diversity (using space--time block codes) can provide. Expressions for the error rates and spectral efficiencies for uncoded constant- and variable-rate transmission are derived, and the dependence on the number of users, the feedback delay, and the link diversity order is investigated. These expressions also apply to Rake reception combined with transmit or receive antenna selection.},
  author       = {Florén, Fredrik},
  issn         = {1402-8662},
  keyword      = {Telekommunikationsteknik,Telecommunication engineering,Elektronik och elektroteknik,Electronics and Electrical technology,feedback,multiuser communication,diversity,throughput,packet radio networks,Interference,frequency hop communication},
  language     = {eng},
  pages        = {218},
  publisher    = {Department of Electroscience, Lund University},
  school       = {Lund University},
  title        = {Aspects on Interference and Diversity in Wireless Networks},
  volume       = {54},
  year         = {2005},
}